Systems and techniques for changing the perspective of a visible image in producing a resultant image, or systems and methods of transforming an image from one perspective form to another have been the subject of scientific thought and research for many years. For example, an early work entitled "A Treatise on the Curvilinear Perspective of Nature and its Applicability to Art" by Herdman indicates that linear perspective is not in agreement with the way humans actually perceive the universe. Herdman suggests that curvilinear perspective is in closer agreement with nature. Herdman discloses techniques for constructing images by mapping image points onto curves rather than mapping points onto lines vanishing to a point as is done when employing conventional linear perspective techniques.
Other systems and techniques for transforming visible images can generally be divided into three separate categories: 1) perspective generation systems and methods suitable for applications such as flight simulators; 2) three-dimensional (3D) to two-dimensional (2D) conversion systems and methods; and 3) miscellaneous systems and methods.
The first category includes U.S. Pat. No. 3,725,563, which discloses a method of and apparatus for raster scan transformations using rectangular coordinates which are suitable for electronically generating images for flight simulators and the like. More specifically, the patent discloses a technique for raster shaping, whereby an image containing information from one viewpoint is transformed to a simulated image from another viewpoint. On the other hand, U.S. Pat. No. 4,763,280 discloses a curvilinear dynamic image generation system for projecting rectangular coordinate images onto a spherical display surface. In the disclosed system, rectangular coordinates are converted to spherical coordinates and then the spherical coordinates are distorted for accomplishing the desired simulation of curvature.
U.S. Pat. No. 4,660,157 discloses a real-time video perspective digital map display method wherein compressed data stored in the frequency domain is interpolated and displayed as a three-dimensional image based on airplane orientation and altitude. In addition, U.S. Pat. No. 4,489,389 discloses a real-time video perspective digital map display including a memory for storing digital data representing a two-dimensional pattern of elevation information, circuitry for generating height and location of a viewing point, circuitry for reading out elevation data out of memory, and perspective transformation circuitry for transforming elevation data into pixel data specifying a pixel location in a perspective display.
U.S. Pat. No. 3,060,596 discloses an electronic system for generating a perspective image using a planar image of a plan view with respect to a viewpoint positioned at a known spot and elevation above the plan view. U.S. Pat. No. 4,474,501 discloses optical simulation of scenic translation using a plurality of parallel image strips.
The second category of systems and techniques perform 3D-to-2D conversion, or vice versa. For example, U.S. Pat. No. 4,821,209 discloses a method of and apparatus for data transformation and clipping in a graphic display system, wherein data transformation is accomplished by matrix multiplication. On the other hand, U.S. Pat. No. 4,667,236 discloses a television perspective effects system for providing perspective projection whereby each point of a three-dimensional object is projected onto a two-dimensional plane. New coordinates X' and Y' are prepared from the original coordinates X, Y and Z, and the viewing distance D, using the general formulas X'=XD/Z and Y'=YD/Z. As the object to be displayed is rotated around the X or Y axis, the viewing distance D is changed for each point.
U.S. Pat. No. 4,721,952 discloses an apparatus for and process of graphically representing three-dimensional objects in two dimensions. In particular, a three-dimensional object is illustrated by a plurality of parallel surface sections, where each surface section is offset from the adjacent sections by a prescribed perspective offset. Another method is disclosed in U.S. Pat. No. 4,752,828, which describes a method of producing geometrical transformations on a video image. In particular, an original image can be transformed into a transformed image by matrix multiplication with respect to the origin of a reference plane.
U.S. Pat. No. 4,819,192 discloses a method of displaying images wherein a three-dimensional object is displayed on a two-dimensional raster scan device. More specifically, the method includes the steps of dividing the surface of an object into a plurality of triangular surfaces, determining data with respect to the three apexes, and transforming the apex data as determined with respect to an observing point into second sets of three apexes. Additionally, U.S. Pat. No. 4,127,849 discloses a system for converting coded data into display data wherein three-dimensional data is converted into two-dimensional data. In particular, a three-dimensional matrix is projected onto a plane to form a two-dimensional dot matrix or line matrix, which can be subsequently converted into a linear array.
U.S. Pat. No. 4,734,690 discloses a method of and apparatus for spherical panning wherein a three-dimensional object located at the view motion center of a spherical space can be viewed from a plurality of viewpoints defined by latitude and longitude data. U.S. Pat. No. 4,754,269 discloses a method of and apparatus for transforming three-dimensional coordinates of a perspective view into two-dimensional coordinates suitable for display on a CRT. According to one aspect of the apparatus, the CRT image can be rotated to simulate a change in the viewpoint with respect to the simulated three-dimensional object. A three-dimension to two-dimension algorithm is also disclosed.
In the third category, miscellaneous systems and methods are disclosed by, for example, U.S. Pat. No. 5,027,287, which describes a device for the digital processing of images to obtain special geometrical effects wherein digital image data corresponding to intersection points on a rectangular X, Y grid are transposed by interpolation with respect to intersection points of a curved surface. U.S. Pat. No. 4,882,679, on the other hand, discloses a system and associated method of reformatting images for three-dimensional display. The disclosed system is particularly useful for generating three-dimensional images from data generated by diagnostic equipment, such as magnetic resonance imaging.